1. Field of the Invention
The present invention relates to backlighting a liquid crystal display device, and more particularly, to a bottom frame for a liquid crystal display (LCD) device, backlight assembly and LCD device using the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for providing a space in a backlight assembly to improve durability, assembling characteristics and protection against heat.
2. Discussion of the Related Art
A related art liquid crystal display (LCD) device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite alignment direction as a result of their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by applying an electric field across the liquid crystal molecules. In other words, as the intensity or direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Since incident light is refracted based on the orientation of the liquid crystal molecules due to the optical anisotropy of the liquid crystal molecules, images can be displayed by controlling light transmissivity.
The LCD device includes a liquid crystal panel and a backlight assembly. The liquid crystal panel includes two substrates spaced apart and facing each other, and a liquid crystal layer interposed between the two substrates. Each of the substrates has a transparent electrode, and the backlight assembly provides light into the liquid crystal panel from a rear side of the liquid crystal panel. Voltage is applied to each of the transparent electrodes such that an electric field is induced between the transparent electrodes. The alignment of the liquid crystal molecules and transmittance of the light emitted from the backlight assembly are changed by varying the intensity or direction of the electric field. Thus, the LCD device displays images by varying the intensity or direction of the induced electric field.
An active matrix LCD device has been widely used, because the active matrix LCD device has sufficient switching speed to display moving color images. The pixels of an active matrix LCD device are arranged in a matrix. Each of the pixel units include a switching element, such as a thin film transistor. The active matrix LCD device uses the thin film transistor in each of the pixel units as a controller for the pixel unit. The active matrix LCD device can have a backlight assembly that includes a cold cathode fluorescent lamp or an exterior electrode fluorescent lamp as a light source.
Generally, the backlights for LCD devices are divided into side type and direct type depending on the location of the light source relative to the liquid crystal panel. In the side type, a light guide plate is disposed at a rear side of the liquid crystal panel and light is emitted from a light source at a side surface of the liquid crystal panel that is redirected into the liquid crystal panel by the light guide plate. In the direct type, light from a backlight assembly, which is disposed at a rear side of the liquid crystal panel, is supplied directly into the liquid crystal panel from the rear side of the liquid crystal panel. An LCD device having a direct type backlight is widely used in large-sized TVs, computer monitors and so on, because the LCD device having a direct type backlight displays bright images.
FIG. 1 is an exploded perspective view of a liquid crystal display device having a direct type backlight according to the related art. The LCD device includes several elements such as a liquid crystal panel 10, a backlight assembly 20 and mechanical elements. The mechanical elements modularize the LCD device. The liquid crystal panel 10 and the backlight assembly 20 are spaced apart and face each other. A main frame 40, such as a rectangular frame, wraps the side surfaces of the liquid crystal panel 10 and the backlight assembly 20. A bottom frame 50 is combined with the main frame 40 from underneath the backlight assembly 20 so that an exterior of the LCD device is supported and a light loss is prevented. A top frame 60, which wraps around front edge portions of the liquid crystal panel 10, is combined with the main frame 40 and the bottom frame 50 so that the LCD device is packaged as module.
A printed circuit board 12 is disposed on at least one side edge of the liquid crystal panel 10. A driving integrated circuit (not shown) is connected to the printed circuit board 12. The backlight assembly 20 includes a reflecting sheet 22, a plurality of fluorescent lamps 24, a couple of side supports 26 and a plurality of optical sheets 28. The reflecting sheet 22 covers inner sides of the bottom frame 50. The fluorescent lamps 24 are disposed parallel to each other within the reflecting sheet 22. A pair of side supports 26 are provided on opposite sides of the bottom frame 50 to affix the reflecting sheet 22 and the fluorescent lamps 24 to the bottom frame 50. The plurality of optical sheets 28 is disposed at an uppermost portion of the backlight assembly 20. Thus, light emitted from the fluorescent lamps 24 is treated to have a uniform brightness after passing through the plurality of optical sheets 28 such that a planar light is supplied to the liquid crystal panel 10.
A backlight assembly and LCD device using light emitting diode (LED) lamps instead of fluorescent lamps as a light source have been introduced, and the use of LED lamps has several advantages. When an LCD device uses LED lamps as a light source, the LCD device has greater brightness than an LCD device using fluorescent lamps. Thus an LCD device using LED lamps can easily display moving images. Also, because an inverter is not necessary, a driving integrated circuit of a backlight assembly using LED lamps has a simpler structure than a driving integrated circuit for fluorescent lamps.
FIG. 2 is an exploded perspective view of a liquid crystal display device using LED lamps in a backlight according to the related art. A backlight assembly 30 includes LED lamps 33, metal core printed circuit boards (MCPCBs) 32, a reflecting sheet 34, a transparent window 36, and optical sheets 38. The backlight assembly 30 uses the LED lamps 33 as a light source.
The LED lamps 33 are disposed on each of the plurality of MCPCBs 32. The MCPCBs 32 are arranged on an inner surface of a bottom frame 50 and have a stripe shape. As shown in FIG. 2, the MCPCBs 32 are connected together via wires 39 between the MCPCBs 32.
A reflecting sheet 34 covers the plurality of MCPCBs 32 and the inner surfaces of the bottom frame 50. The reflecting sheet 34 has through-holes 35, each of which corresponds to one of the LED lamps 33, respectively. Thus, the LED lamps 33 protrude through the through-holes 35 in the reflecting sheet 34, respectively. The MCPCBs 32 are typically attached to the inner surface of the bottom frame 50 to hold the MCPCBs 32 in position such that the LED lamps 33 are properly positioned to protrude through the reflecting sheet 34.
Optical sheets 38 are disposed over the reflecting sheet 34 and the transparent window 36 is interposed between the optical sheets 38 and the reflecting sheet 34. The transparent window 36 has reflecting dots 37 corresponding to the LED lamps 33, respectively. Light, which is directly emitted from the plurality of LED lamps 33 or reflected by the reflecting sheet 34, is dispersed by the reflecting dots 37 of the transparent window 36 and changed into a planar light source for the liquid crystal panel 10. The LED lamps have outstanding optical properties and structural characteristics. Further, the backlight assembly using LED lamps includes similar mechanical elements as those in the backlight assembly using fluorescent lamps.
In FIG. 1, for example, a couple of side supports 26 not only affix the fluorescent lamps 24 to the bottom frame 50 but also protect a clip socket or a soldering portion by covering the clip socket or the soldering portion, which is a connection between electrodes at the edges of the fluorescent lamps 24 and the driving integrated circuit of the backlight assembly. However, as shown in FIG. 2, the couple of side supports 26 only aid in defining a space, in which the LED lamps are disposed on the bottom frame 50. Although the LED lamps radiate heat during operation, the bottom frame according to the related art in FIG. 2 does not have a provision for heat release or heat removal. Further, the MCPCBs 32 in the related art shown in FIG. 2 are difficult to replace because a defective MCPCB 32 has to be detached from the inner surface of the bottom frame 50 and the wires 39, and then a new MCPCB 32 has to be properly positioned, attached to the inner surface of the bottom frame 50 and rewired. Further, since the additional element of a transparent window interposed between the LED lamps and the plurality of optical sheets is required, the process of fabricating an LCD device with a backlight using LED lamps is more complicated than a LCD device with a backlight using fluorescent lamps.